The present invention relates to methods for detecting a dosing error of a reduction agent in a delivery module of an SCR catalytic converter system. The present invention, furthermore, relates to a computer program which carries out every step of the methods according to the invention when it is executed on a computer, and to a machine-readable storage medium, which stores the computer program. Finally, the invention relates to an electronic control unit, which is equipped in order to carry out the methods according to the invention.
Today, the SCR (selective catalytic reduction) method is utilized in the aftertreatment of exhaust gases in order to reduce nitrogen oxides (NOx) in the exhaust gas. The SCR method is predominantly employed in motor vehicles. There, a urea-water solution (HWL), commercially also known as AdBlue®, is introduced into the oxygen-rich exhaust gas. For this purpose, a dosing module is used which comprises a nozzle in order to spray the HWL into the exhaust gas flow. Moreover, a dosing valve is implemented which can control the flow through the dosing module. In the SCR catalytic converter system, the HWL reacts to form ammonia which subsequently bonds with the nitrogen oxides, from which water and nitrogen is created. The HWL is pumped via a delivery module from a tank to the dosing module. In addition, the delivery module is connected to the tank via a return so that excess HWL can be returned. An orifice plate or choke in the return controls the return flow.
The supplied quantity of HWL in the exhaust gas has consequences for the functioning of the SCR catalytic converter system. For this reason, a dosing error of the HWL influences the nitrogen oxide emission.
DE 10 2009 000 061 A1 relates to a method for reducing quantity tolerances of a dosing device of an SCR catalytic converter system. Because of aging, errors in the reagent dosing occur in the dosing device. These errors manifest themselves in over- and under-dosing of the reduction agent, which in turn leads to an infringement of the emission limits. With the help of the described method it is possible to detect deviations between the demanded target quantities and the actual quantities dosed and to take these into account by way of suitable regulating in a control unit, which then corrects the dosing quantities by way of activation intervals of a dosing pump. The basic idea of the method is to detect the mass flow of the reagent in the reagent pressure line, for example between the dosing pump and a dosing nozzle.
DE 10 2013 218 553 A1 relates to a method for operating a hydraulic delivery and dosing system for an SCR catalytic converter system. For the dosing to suit requirement a delivery pump of such a system delivers a desired or required quantity of reagent solution from a tank. The reagent solution is fed in a system pressure region into a pressure line and is sprayed into the exhaust gas system via a dosing unit, which can comprise one or a plurality of dosing valves. The system therefore has to be operated at a preset system pressure or in a presettable system pressure range. In the method it is provided that even during a pressure build-up in the system the pressure profile is subjected to a plausibility check to determine if a substantially continuous pressure increase is detectable. Thus, the pressure build-up is continuously monitored and evaluated, so that an error in the system can be very quickly detected.